F.3.1 Basic Principles
In North America (United States, Canada, and Mexico), PI codes are based on call letters rather than being assigned by any national organisation, as is done in countries throughout the rest of the world. A portion of the PI codes are reserved for network usage and also for assignment to stations in Canada and Mexico.
The CENELEC RDS standard accepts the usage of coverage area codes for all possible PI codes (see Section F.2 above on coverage area codes). Within North America coverage, area codes are only recognised in the following range of PI codes:
• B_01 to B_FF hex
• D_01 to D_FF hex
• E_01 to E_FF hex
All other PI codes do not make use of coverage area codes and must be handled as such within the receiver.
Some current European receivers store PI codes into presets in addition to storing frequencies into presets. This function is to recognise the broadcast first by programme rather than frequency. Thus, if a preset is pushed and the PI code has changed, the European RDS receivers would not recognise the new PI code and go into a PI search.
A technical publication from the EBU states:
If, however, the PI code changes completely, the receiver should initiate a PI search for a frequency whose PI code exactly matches the PI code of the original tuned frequency. Failing an exact PI code match, the receiver should search for a PI code differing only in the regional element (b11to b8) from the original PI code. If neither of these criterion are met, the receiver should remain on the original tuned frequency.
Therefore, since call letters are used to create the PI code, the receiver would have to do a PI search every time a station would change call letters or a preset is pushed in a new listening area having a station at the same frequency as
286 RDS: The Radio Data System
the preset station. For PI codes smaller than B000 hex, future receivers could check the AF list associated with a preset and if no AFs are acceptable, a PI search could be initiated. If no identical PI is found, the receiver should return to the original tuned frequency and accept the new PI code.
If a PI search is performed, the regional variant search (the second search to match PI codes, differing only in b11 to b8) should be eliminated in a PI search if the tuned PI is below B000 hex, or within the ranges of C001 to CFFF hex and F001 to FFFF hex.
If a feature similar to European regional variants is desired, a grouping in the B, D, and E blocks could be designated as follows. If NPR broad- casts break off national programming to go local for a period of time, it could be assigned a PI of B_01. Note that you cannot use 0 as the second nibble because current receivers will not search for AFs. Therefore, use 1–8 to F for indication of a “regional” variant. If no AFs or identical PIs are found via the AF list or an identical PI search, the receiver could, while tuned to NPR station 1 (PI= B101) accept a variant NPR station 2 whose PI varies only in the second nibble (bits 5–8). Thus B201, B301, B401, …could be accepted.
PI codes starting with the B, D, and E nibbles yield 765 possibilities for
“regional” programming. These PI codes will be shared by the United States, Canada, and Mexico. The problem here becomes that a “telephone book”
needs to be kept; however, there should not be too many broadcasts that fit in this category and not many would be used.
F.3.2 Call Letter Conversion Method
The call letter conversion method to be used is described in detail in the RBDS standard, Annex D, Section 6.1. It makes uses of a conversion table and some simple algorithms. The details required to make the conversion are, however, so extensive that they cannot be quoted in this book, and only the RBDS standard itself can help here in proceeding with the conversion of a particular case.
The rules that are spelled out in the RBDS standard could also be implemented in encoder software so that the station that wants to use RDS can simply enter its call letters and subsequently the encoder would then make the PI code assignment in full compliance with these rules. The broadcast station interested in this matter should discuss this issue with the encoder supplier to avoid any error or misunderstanding.
Appendix F 287
References
[1] CENELEC EN 50067:1998 - Specifications of the Radio Data System (RDS.) for VHF/FM broadcasting European Committee for Electrical Standardisation (CENELEC), 35B rue de Stassart, B-1050 Brussels, April 1998.
[2] EIA/NAB(1997), National Radio Systems Committee: United States RBDS Standard version 2.0, Specification of the Radio Broadcast Data System (RBDS).
[3] EBU, Guidelines for the implementation of the RDS system, Tech. 3260-E, Jan. 1990.
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Appendix G
Appendix G
RDS Country or Area Identification Codes